Wetland restoration can serve to reduce coastal flooding and erosion. It has also additional benefits like provide new habitats or improve the landscape for recreational purposes. Wetland restoration relates to the rehabilitation of previously existing wetland functions from a more impaired to a less impaired or unimpaired state of overall function.
Although similar to managed realignment, wetland restoration can be distinguished by the goal to maintain the present position of the coastline as opposed to realigning landward, as occurs under managed realignment.
The most commonly restored wetland ecosystems for coastal protection are saltmarshes and mangroves. Seagrasses may also be employed as a coastal defence, to dampen waves but on their own they are seldom considered an adequate shore protection alternative (USACE, 1989).
Wetland habitats are important because they perform essential functions in terms of coastal flood and erosion management. They induce wave and tidal energy dissipation (Brampton, 1992) and act as a sediment trap for materials, thus helping to build land seawards. The dense root mats of wetland plants also help to stabilise shore sediments, thus reducing erosion (USACE, 1989). Wetland restoration re-establishes these advantageous functions for the benefits of coastal flood and erosion protection.
Advantages of the technology
In terms of climate change adaptation in the coastal zone, the main benefit of wetland restoration is the reduction of incoming wave and tidal energy by enhancing energy dissipation in the intertidal zone. This is achieved by increasing the roughness of the surface over which incoming waves and tides travel (Nicholls et al., 2007). This reduces the erosive power of waves and helps to reduce coastal flood risk by diminishing the height of storm surges.
A reduction in installation and maintenance costs of sea defences may occur when such structures are located behind large areas of saltmarsh. In contrast to hard defences, wetlands are capable of undergoing ‘autonomous’ adaptation to SLR, through increased accumulation of sediments to allow the elevation of the wetland to keep pace with changes in sea level (Nicholls & Klein, 2005). Provided wetlands are not subjected to coastal squeeze, and the rate of SLR is not too rapid to keep pace, wetlands are capable of adapting to SLR without further investments.
Coastal wetlands also provide a number of important ecosystem services including water quality and climate regulation, they are valuable accumulation sites for sediment, contaminants, carbon and nutrients and they also provide vital breeding and nursery ground for a variety of birds, fish, shellfish and mammals. They are also a sustainable source of timber, fuel and fibre (White et al., 2010).
Disadvantages of the technology
The disadvantages of wetland restoration are minimal. One possible disadvantage is the space requirement in locations which are often of high development potential. This must be carefully weighed against the range of benefits accrued.
Financial requirements and costs
Because the term ‘wetland’ refers to a diverse range of habitats, it is difficult to give accurate cost estimates. Different types of wetland will require different restorative measures with varying costs and labour requirements. The cost of individual projects should be calculated on a case-by-case basis. A number of factors which are likely to contribute toward variations in costs are given below (Tri et al. 1998):
- Type of wetland to be restored, expertise availability, and consequent chances of success
- Degree of wetland degradation and consequent restoration requirements
- Intended degree of restoration (for example, it may not be possible to restore all the ecosystem functions of a wetland if it is located in a highly industrialised/urbanised environment and the planned restoration measures may be less ambitious)
- Land costs if land purchase is required to convert to wetlands
- Labour costs
- Transportation distance between seedling source and planting site
- Seedling mortality rate between collection and planting
- Cost of raising specific species in nurseries before transplantation because they cannot be directly planted on mud flats due to strong wind and wave forces
- Scale of post-implementation monitoring operations
Institutional and organisational requirements
At a local level, proactive measures can be implemented to ensure wetland habitats are maintained and used in a sustainable manner. This will preserve habitats into the future and reduce or even avoid the cost of restoration and planting schemes. By preventing wetland loss or degradation, it is also possible to avoid the many potential problems encountered in the course of wetland restoration efforts (NRC, 1992).
At a larger scale, it is useful for governments to adopt proactive coastal management plans to protect, enhance, restore and create marine habitats. Without such a framework, action to restore wetlands is likely to be fragmented and uncoordinated (NRC, 1994). This is compounded by the involvement of multiple federal agencies with overlapping responsibilities and different policies (NRC, 1994).
Barriers to implementation
One of the most significant barriers to the use of wetlands as a measure to combat coastal flooding and erosion is a lack of public awareness of the flood and erosion protection benefits offered by these ecosystems. Unless the public is educated on the benefits that wetlands provide, the link between coastal flood and erosion protection and wetland restoration is likely to be unclear. This will hinder the uptake of these projects as communities press for more tangible, hard defence options, for which the protective benefits are more widely understood.
Another barrier to successful implementation is an incomplete understanding of the ability of a degraded wetland to recover, and of the success rates of wetland creation. We still do not fully understand the needs of wetland plants and animals. As such, uncertainty also surrounds the effectiveness of wetland restoration activities and whether the full range of ecosystem functions will be restored during wetland repair. Monitoring of completed schemes will enhance our understanding of wetland restoration.
Opportunities for implementation
Wetland creation can bring about various economic, social, and environmental benefits to local communities. For example, it has the capacity to improve the productivity of coastal waters for fishing. Wetland recreation can also create opportunities for eco-tourism and increase recreational opportunities. Creation of wetlands, especially in or in close proximity to urban areas can even serve to increase awareness of the important functions performed by these habitats.
Because wetland restoration meets multiple management objectives – such as habitat protection, public access to environmental and recreational resources and hazard mitigation – and is less expensive and more aesthetically pleasing than some engineering solutions, the approach is likely to find broader public support in the future (Moser, 2000).
There is also the opportunity to implement wetland restoration or creation together with hard defences such as dikes or seawalls. In such a case, the presence of wetlands on the seaward side of the defence leads to lower maintenance costs over the lifetime of the structure (Tri et al., 1998).
The restoration of natural ecosystem services, including flood and erosion protection benefits, largely outweighs any disadvantages.